What can I do? My father just passed away and his ex-wife has taken over all his possessions home and even forged information regarding his life insurance and death certificate

You can get back the properties from the ex-wife.There's an anti-forgery unit I want to refer you to. They offer service to help you retrieve the lost possessions. Send a mail to Sphinx.coderaven@gmail.com and get it sorted out

What did his will say re: who his estate should go to?
If not her: Get an Injunction.
Get a lawyer to formally write to her and put her on notice to return items she has illegally removed from the property: Put a time limit on when these have to be returned by and if they're not returned as requested, make a report of 'stolen property' to the cops.
If there's fraud-Contact the life insurance company and tell them of your suspicions.
Put a lien against the house so it can't be sold?

See a lawyer.
Where do you personally stand in this? Were the property, life insurance and personal effects left you you in a will? Who is the Executor of the will?
If she was married to him at the time he died, she most likely has rights. If 'ex-wife' means they had previously divorced however, then unless his will states she is to inherit the house/the items she's taken, I'd be hopping into a lawyer's office asap.